Final answer:
One of the oldest varieties of wheat likely has chromosomes from three different species due to allopolyploidy, where chromosome sets from different species are combined. Bread wheat, a hexaploid, has 42 chromosomes originating from hybridizations that included einkorn wheat and Aegilops species. This adaptation, which took place less than 10,000 years ago, has enhanced wheat's diversity and resilience.
Step-by-step explanation:
The most likely reason that one of the oldest varieties of wheat has chromosomes from three different varieties is due to a natural process known as allopolyploidy. Allopolyploidy involves the combination of chromosome sets from different species through hybridization, resulting in organisms with multiple sets of chromosomes, a condition known as polyploidy. Bread wheat, in particular, is a product of such a process, where it combines the genomes from einkorn wheat and two different Aegilops species, resulting in a hexaploid organism with chromosomes from three ancestral species. Each genome consists of seven chromosomes, thus diploid cells of bread wheat possess 42 chromosomes. This phenomenon is quite recent in evolutionary terms, having occurred less than 10,000 years ago, and it has been a beneficial adaptation for the wheat species.
The polyploidy in wheat has contributed significantly to the diversity and adaptability of the crop. This mechanism of adaptation has led to the formation of what we now know as bread wheat, which is essential for agriculture. Moreover, the uniformity in major crops like wheat makes the genetic diversity from wild crop relatives crucial for resistance against diseases and pests.